The present invention is not concerned with networks of data processing servers or nodes whose only function is the carrying out of asynchronous communications. Rather, the present invention is directed to multinode data processing networks which exhibit or require time synchronization. This synchronization is important when it comes to file sharing operations to insure that the order in which data is read from and written into files is consistent with the intentions of system users. To this end the assignee of the present invention has provided software and hardware facilities to accomplish these goals. In particular, one may employ a device identified as the IBM 9037 Sysplex Timer or ETR (External Time Reference). Because of the high speed of modern data processing systems, timing synchronization is typically set to be such that the differences in time lie at the submicrosecond level.
Against these demanding time considerations, it still happens that in the course of network operation it may become useful or desirable to change one or more aspect of the timing information that is exchanged in the network. The changes addressed here are one that are driven by external factors, such as the desire of the system operator to change time zones or the desire to change the timing to account for local variations and adoptions made for such things as “Daylight Savings Time.” The communications that are used to match timing information in disparate systems should be reliable.
Use of a time reference such as the 9037 Sysplex Timer, provides this reliability; the data processing servers in the network thus have a dedicated direct connection for the sole purpose of forwarding timing information to that system. In this system, directly attached data processing components continually monitor each individual timing related information field to determine if it has been updated. This involves the use of processing power at each node in the network to detect changes in the timing parameters. The timing information typically includes an ETR network identifier, a leap seconds offset and a total time offset, which is the sum of the time zone and daylight savings time offsets. Scheduled updates are viewed at the ETR console and not at each individual system in the timing network. Lastly, if a node loses all communication with the ETR, the parameter data is considered to be invalid at that point in time.
It is thus seen that it is not only desirable to have the nodes in a data processing network synchronized to a desired degree of accuracy, but that it is also desirable to be able to have a new server join the network in a safe and secure fashion. The process of having a server leave a network is not as difficult, though it is still important to maintain synchronization while time dependent processes are running and interacting with one or more server nodes.